Conventionally there is known an optometric apparatus including independently an optical system for a right eye for projecting a chart for the right eye and an optical system for a left eye for projecting a chart for the left eye, in order to inspect visual function of both eyes of an examinee. For example, in a subjective device for inspecting vision or eyesight, if vision of the right eye of the examinee is measured, a chart of a Landolt ring or the like is projected by the optical system for the right eye, if the vision of the left eye is measured, a chart is projected by the optical system for the left eye and if visions of both eyes are measured, the same charts are projected by the optical systems for the right and left eyes.
By the way, accommodation and convergence are increased/decreased together in the daily life and appear to have an un-separable relation with each other, but actually the convergence is increased and decreased while maintaining constantly the accommodation or the accommodation can be changed to certain degree while maintaining the convergence constantly. For example, phenomenon for changing only the accommodation while doing a single distinct vision of a target means a relative accommodation, a scope between both extremes in which the single distinct vision is eventually impossible by increasing gradually a degree or power of a concave and convex wear lens means a relative accommodation region, and the fact shown in a degree or power of the lens means a relative accommodation power (area). Moreover, when wearing to the both eyes or one eye a prism whose base is disposed outward or inward, instead of a spherical lens, phenomenon of obtaining the single distinct vision by overcoming the prism means a relative convergence, the fact of showing this with a degree of convergence means a relative convergence power (width). However, even in a scope that the relative accommodation and the relative convergence are possible, there is a case comfortable to view with the both eyes, it is known that a relationship between the accommodation and the convergence at that time in a healthy people are positioned on the Donders convergence line (see Document 1). On the other hand, when looking an instrument such as a telescope or binoculars, there is appeared generally a phenomenon of an instrumental near sight in which visual accommodation is in a side of the near sight, while, it is known that the instrumental near sight represents a value of −0.5 D to −1 D based on a visual axial angle, a power of adjustment pursuant to the age, a size of visual field, brightness of the visual field, a state of refraction and so on in case of monops or single eye and binocle or both eyes and binocular observation, and the relationship between the accommodation and the convergence tends to separate from the Donders convergence line (see Document 2 as described hereinafter).
[Document 1]
Editor: Akira Ogiwara “Physiology of Eyes” Igaku-Shoin pp. 358-365, 1966
[Document 2]
Editors: Nin Ohotsuka, Shinichi Kano “Rinnshou Ganka Zensyo, No. 20 Vols.” Eye Function III Kanahara Syuppan pp. 462-463, 1970
Accordingly, in the optometric apparatus as described above, if it is desired that the visual function of the both eyes is inspected on the assumption that the different charts are projected by the optical systems for the right and left eyes, and the charts are recognized as one chart with the both eyes, there is a case that the examinee occurs an adjustment by the instrumental near sight, the relationship between the accommodation and the convergence separates from the Donders convergence line and the projected charts of the optical systems for the right and left eyes are viewed to the examinee into a rightward and leftward and unstable rocking condition. Otherwise, if the examiner has an oblique position which is no problem in the daily life, despite it is desired that the an inspection is proceeded without considering the oblique position, normally, the fusion of the projected charts of the optical systems for the right and left eyes are not performed due to the oblique position and as a result there is a problem that the charts are viewed to the examinee in a deviated condition.
Even though the same charts are projected by the optical systems for the right and left eyes, because the charts are one body substantially, the examinee does not have appreciation of seeing a near position when near point inspection for vision, for example, if the examinee has the oblique position there is a case that the both eyes are not converged and the fusion is not performed. Furthermore, even if the both eyes converge when performing the near point inspection for vision, if the relationship between the accommodation and the convergence separates from the Donders convergence line, there is a problem that the fusion of the projected charts of the optical systems for the right and left eyes is also not performed easily and the examinee often has a whole of a time for inspection, actually.
The present invention is made in view of the above circumstances and it is an object to provide an optometric apparatus in which projected charts of optical systems for right and left eyes are prevented from viewing in a deviated sate, and an optometric chart used for the optometric apparatus.